Device for hooking pieces, in particular printed circuits, on transport lines present in tunnel type kilns and the like

ABSTRACT

A device for the hooking of printed circuits includes a support constituted by a roughly U-shaped structural shape with a seating designed to allow the insertion of the printed circuit, one or more pins inserted into holes in one wall of the structural shape, and thrust systems designed to push the pins against the opposite wall of the structural shape, and devices designed to engage the thrust systems in order to retract the pins and allow the insertion of a printed circuit.

BACKGROUND OF THE INVENTION

This invention relates to a device designed to hook pieces, inparticular printed circuit boards, onto transport lines present intunnel kilns or similar kilns.

The device in accordance with the invention can be classified among theequipment used to manufacture electronic cards or printed circuits, andin particular among the equipment used during the circuit firing stagein a kiln.

DESCRIPTION OF THE RELATED ART

The manufacture of printed circuits such as those of computer boardsuses photographic processes to make the tracks or pattern of the circuiton a base plate, which consists of one or more layers of copper or otherconductive material.

For this purpose a layer of material sensitive to ultraviolet light, forexample, is spread on the plate; that layer is photographically exposed,and the plate is then introduced into baths that dissolve the unexposedlayer and the underlying layer made of conductive material to producethe circuit tracks.

These known procedures comprise various stages including the stage whenthe said sensitive layer is fired, during which the plates thatconstitute the circuit base are introduced into a kiln, usually thetunnel type, in which the coating layer is “fired”.

For the purpose of firing, each card is passed one or more times througha tunnel kiln together with other similar cards.

The existing conveyor equipment for the firing of rigid printed circuitsallows the circuit boards to be introduced in succession into supportsconstituted by structural shapes arranged transversely on a conveyorbelt situated in the lower part of the route, so that the boardsmaintain a vertical position as they advance through the kiln.

This type of equipment, which is used to handle basically rigid printedcircuits, does not need to be fitted with restraint and grippingmechanisms, and is consequently unsuitable to support or move the morerecent flexible circuits, as in this case the boards cannot maintain avertically leaning position, and must therefore be hung from a transportline installed in the upper part of the tunnel and fitted with grippingjaws.

The main drawback encountered with the use of known systems for thetransport of flexible printed circuits is that they use complex, bulkyjaw assemblies, each of which is associated with pneumatic drivedevices; this increases the cost of manufacture and also restricts thenumber of printed circuits that can be hung from the conveyor, due tothe excessive bulk of these gripper activation devices.

SUMMARY OF THE INVENTION

The invention provides a new gripping system for the advance of flexibleprinted circuits through a tunnel kiln or the like, the main objectiveof which is to reduce the complexity of manufacture, thus limiting bothproduction costs and overall dimensions, as the components of thehooking parts are simplified.

The immediate advantage of the proposed system is that the reduction inoverall dimensions leads to a considerable increase in the carryingcapacity of the conveyor line and in the number of circuits that can betreated simultaneously on the same line.

A further advantage of the innovation in question is that it features anew gripping system which eliminates components secured by screws orother screwing systems; such components, which are present in knownhooking devices, can generate critical situations such as breakage orjamming of the gripping parts when they pass through the kiln at hightemperature.

These particular purposes, advantages and functions are all achieved, inaccordance with this invention, by a device for hooking pieces, inparticular printed circuits, to transport lines present in tunnel kilnsand the like, in accordance with which shaped supports are fittedtransversely to a conveyor belt, slat conveyor or the like, the saidsupports being constituted by roughly U-shaped guides fitted withelastic systems designed to maintain in the thrust position a pair ofpins with sharp corners at the ends, which constitute the elements thatgrip the printed circuit.

The said elastic systems, subjected to the action of pistons whichcontrol their movement, enable the said pins to be maintained in thethrust position during the stages of gripping the circuit, and retractedfor a certain distance during the loading and unloading stages.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and details of this invention will emerge moreclearly from the following description of a preferable form ofmanufacture, illustrated by way of example but not of limitation in theannexed drawings in which:

FIG. 1 shows the schematic side view of a tunnel kiln in which a printedcircuit loading line fitted with gripping elements in accordance withthe invention is installed

FIG. 2 represents a schematic view from below of one of the structuralshapes designed to restrain a printed circuit

FIG. 3 illustrates a detail of the structural shape in question incross-section, in the direction of arrow III—III in FIG. 2

FIG. 4 shows a schematic front view of one of the structural shapes onwhich a printed circuit has been mounted.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows printed circuits received from a car through opening F of atunnel kiln 1 are hung from a conveyor line 2 in the upper interior partof the kiln, pass through the tunnel in which they undergo a firingprocess, and are picked up by a second car at exit F′ and sent to thetin immersion cycle.

The characteristic feature of the invention is that it uses grippingsystems which are simple, cheap and compact but highly functional. Whenfitted at regular intervals along conveyor 2 the gripping systems canrestrain the cards, causing them to advance through the kiln.

The gripping systems 3, are applied and fixed parallel to one another onconveyor 2; they are constituted by a roughly U-shaped metal structuralshape defined by two parallel walls 4 and 5 connected at right angles toa base 6. See FIG. 3.

One of the two parallel walls contains two seatings into which twospecially shaped pins 7, designed to slide axially, are inserted.

The pins have an outer head 8 and an inner end head 9 which has pointedgripping edges.

The ends of an elastic element 10, constituted by a leaf spring made,for example, of music wire, are fitted to outer head 8 of each of pins7; the spring has a retracting central sector which is constrained tostructural shape 3 via the L-shaped brackets shown as 11, which aresecured with screws 12 to base 6.

Leaf spring 10 normally maintains each pin pushed towards the inside ofthe structural shape, so that inner head 9 tends to approach theopposite inner wall of the structural shape elastically.

The spring 10 also has ends 13 flared outwards to facilitate theintroduction of rods 14, constituted by pneumatic piston rods or thelike, which slightly distance the spring from structural shape 3 withconsequent retraction of each pin 7, thus allowing the introduction andremoval of printed circuit 15.

More specifically, rods 14 are activated in such a way that at entranceF to tunnel 1 they are inserted between structural shape 3 and the endsof leaf spring 10 to raise it and allow retraction of pins 7 and theintroduction of the printed circuit into structural shape 3.

At the next stage, rods 14 are retracted to release the elastic thrustaction of the spring on the pins, leading to hooking and restraint ofthe printed circuit 15 introduced into the structural shape.

Once hooked onto the corresponding structural shape 3, each printedcircuit is made to advance by conveyor line 2 through tunnel kiln 1,thus remaining constrained in a hanging position.

A second pair of rods 14 comes into operation at exit F′ from thetunnel; as in the previous case, they are introduced into the two flaredends of the elastic spring and cause pins 7 to retract, so that theprinted circuits are released from the corresponding structural shapes,and can be unloaded into a pick-up car and conveyed to the molten tinimmersion sector.

It is advantageous for the outermost edges of each structural shape 3 topresent flaring 16, which facilitates the introduction of the variousprinted circuits.

As seen, the special design of the structural shapes in accordance withthe invention offers the advantage of simpler manufacture and much morelimited size than known systems, resulting in a considerable increase inthe carrying capacity of the conveyor line and the number of circuitsthat can be treated simultaneously.

In addition, as the presence of equipment secured with screws, which areneeded for the assembly of known gripping jaws, has been totallyeliminated, all risk of breakage or jamming of the gripping parts isavoided, as the said parts, which are subjected to the thrust andrelease action of elastic elements, withstand the high kiln temperatureswithout distortion.

A preferred version of the hooking device in question, designed inparticular for the firing of printed circuits, is described andillustrated, but a number of technically equivalent variations in themechanical parts and components referred to are possible, and should bedeemed to fall within the scope of this invention.

Equally, the materials used can vary in accordance with practicalrequirements.

What is claimed is:
 1. A device for hooking circuits on tunnel transport lines, comprising; a support comprising a U-shaped structural member having a first wall and a second wall and two holes in the second wall, said support having a seat accepting the insertion of a circuit, and an elastic system mounted to the support and adapted to press the circuit against the first wall of the support, the elastic system comprising at least a pair of pins inserted through the two holes, and a bias component mounted on the second wall and arranged to bias pins through the holes and against the first wall, a sharp end of pin adapted to grip the circuit against the first wall, the bias component comprising a leaf spring with a central sector fixed to the structural member, the leaf spring having ends distanced from the structural member to define two insertion spaces, the ends being retractable, upon insertion of drive devices in the insertion spaces, from the structural member and upon retraction providing a force to disengage the pins from against the circuit and the first wall to release the circuit.
 2. The device of claim 1, wherein each of the insertion spaces are shaped to accept a rod.
 3. The device of claim 1, wherein the pins are arranged to slide axially at a right angle to the first wall.
 4. The device of claim 3, wherein the leaf spring elastically biases the pins towards the first wall of the structural member.
 5. A device for hooking circuit boards on a conveyer line, comprising: a support with a seating surface for accepting the insertion of a circuit board and adapted to be mounted on a flexible conveyor; and an elastic means, mounted to a first wall of the support, for pressing the circuit board against a second wall of the support, the support comprising a U-shaped structural member and having two holes in the first wall; and the elastic means comprising at least a pair of pins inserted through the two holes, and a bias component mounted on the first wall and arranged to bias the pair of pins through the holes and against the second wall, the bias component comprising a leaf spring with a central portion fixed to the structural member, the leaf spring having ends distanced from the structural member to define two insertion spaces, the ends being retractable from the structural member and upon retraction disengaging the pins from against the circuit board and the first wall to release the circuit.
 6. The device of claim 5, wherein each of the insertion spaces are shaped to accept a rod, and the pins are arranged to slide axially at a right angle to the first wall. 